Communicating in a wireless network

ABSTRACT

Systems for communicating with a target node, e.g. a particular device, of a wireless network. In particular, there is a concept of accurately identifying a timeout period during which the target node is expected to acknowledge the communication. There is a dynamic timeout period, the length of which is based upon one or more characteristics of at least one most recent or previous communication from the target node.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2019/077010, filed on Oct.7, 2019, which claims the benefits of European Patent Application No.18213296.9, filed on Dec. 18, 2018 and Chinese Patent Application No.PCT/CN2018/109841, filed on Oct. 11, 2018. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to the field of wireless communication technology,and in particular to methods of communicating between nodes of networkswith a low data transmission rate.

BACKGROUND OF THE INVENTION

Wireless networks are becoming increasingly common in everyday life, forexample, to implement the internet-of-things. Wireless networks with lowdata transmission rates are also of particular interest, to minimizecost and energy consumption and to extend radio coverage. One example ofa low data transmission rate network is a Low-Power Wide Area Network(LPWAN), although other examples are known.

A Low-Power Wide-Area Network (LPWAN) has been proposed to fill atechnological gap that exists between the well-known technologies ofwireless sensor networks and high throughput wide area networks. A LPWANis a wireless Wide-Area network technology specialized forinterconnecting devices with only a low bit-rate communicationcapability, over a wide area and with low cost. Typically, a LPWAN isused for battery powered devices, resource-restricted units, orpower-harvesting devices, such as solar-powered devices.

Popular LPWAN technologies include, for cellular applications, theNarrowBand IoT (NB-IoT) radio technology standard or the enhancedMachine Type Communications (eMTC) protocol. Another popular LPWANtechnology is LoRaWAN.

There has been a growing interest in using LPWAN technology in newindustries, especially the automotive, utility (e.g. lighting or water),agricultural and health industries. In these applications, end nodes ofa LPWAN consist of peripheral input and/or output devices, and mayinclude, for example, water meters, gas detectors, car monitoringsystems, personal healthcare monitoring products and/or wirelessluminaires. Typically, end nodes are unable to route receivedinformation to other devices in the LPWAN.

In LPWANs, there has been a growing trend in reducing the powerconsumption of the nodes of the LWPAN, and especially end nodes, e.g. toimprove a battery life and minimize traffic.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention,there is provided a method of communicating with a target node of awireless network. The method comprises receiving a first uplink messagesent by the target node and subsequently sending a downlink message tothe target node. The method further comprises calculating a minimumtimeout period using at least one characteristic of the at least onefirst uplink message, the minimum timeout period representing a minimumlength of time following the sending of the downlink message duringwhich the target node is expected to respond with a response uplinkmessage. The method further comprises determining a timeout period basedon the minimum timeout period. The method also comprises determiningwhether the target node has responded to the downlink message with aresponse uplink message within the timeout period following the sendingof the downlink message.

Thus, a minimum length of a timeout period for receiving a responsemessage, indicating that a target node of the wireless network hasacknowledged or otherwise received a downlink message, is determinedbased on at least one characteristic of one or more previous uplinkmessages (“first uplink messages”) sent by the target node. The firstuplink message(s) is received prior to the issuance of the downlinkmessage. In some embodiments, if a response uplink message is notreceived within the timeout period, the downlink message can be resent.

In other words, a dynamic timeout period for receiving a response uplinkmessage from a target node can be set based on one or morecharacteristics of at least one uplink message recently sent by thetarget node, preferably including at least a most recent uplink messagesent by the target node.

The present invention relies on the understanding that the communicativeability operation of the target node may be restricted or limited (e.g.limited bandwidth, limited duty cycle and so on). Thus, after issuanceof a first uplink message or messages, a target node may be unable tosend a further message, e.g. a response uplink message, until aparticular period of time (the “recovery period”) has passed. Thus, if atimeout period for resending of a downlink message to the target nodeends during the period of time during which a target node is unable torespond (i.e. during the “recovery period”), then it may be incorrectlyassumed (e.g. by an observer or a sender of the downlink message) thatthe target node has not successfully received the downlink message. Thiscould lead to communicative confusion and/or delay. By way of example, adownlink message could be unnecessarily resent (as the target node mayhave successfully received the downlink message, but been unable toacknowledge it).

The present invention therefore proposes to set a length of the timeoutperiod to be based on one or more characteristics of the one or morefirst uplink message(s), preferably including at least a most recentfirst uplink message sent by the target node. It has been recognizedthat characteristics of the first uplink message or messages containinformation about the recovery period (or can be used to calculate therecovery period).

This avoids a timeout period being incorrectly set, which could resultin an (incorrect) assumption that the target node has not received thedownlink message. This assumption may be incorrect, because it may bethe case that the target node has been simply unable to acknowledge thedownlink message due to communicative restrictions.

By way of example only, embodiments may avoid unnecessary reissuance ofa downlink message, minimizing traffic on the wireless network andreducing power consumption whilst also avoiding unnecessarily longtimeouts (e.g. a timeout which would account for all situations), whichwould slow down communication times.

A maximum timeout period may also be determined in a similar manner.

Preferably, the at least one characteristic of the one or more firstuplink messages comprise metadata of the one or more first uplinkmessage. In particular, the at least one characteristic may include oneor more: timing information of the first uplink message(s), a data sizeof the first uplink message(s), a transmission time of the first uplinkmessage(s) and so on.

Preferably, the target node is an end node of a wireless network. Insome embodiments, the downlink message is a command (e.g. for the targetnode to perform a particular action). Commands typically instigate aresponse uplink message, such as an acknowledgment, to be issued by thetarget node.

It will be appreciated that the precise characteristics of the firstuplink message used to determine the minimum length of the timeoutperiod may differ according to different implementation details (e.g.different target nodes or different wireless network systems may employdifferent schemes for operating a target node).

Preferably, the minimum timeout period is calculated using timinginformation and/or a data size of the first uplink message. Thus, the atleast one characteristic of the first uplink message(s) used tocalculate the minimum timeout period may comprise timing informationand/or a data size of the first uplink message.

Timing information may include, for example, a (predicted) time at whichthe first uplink message is sent by the target node, a time at which thefirst uplink message is received, a length of time taken to send uplinkinformation and so on. Preferably, the timing information comprises atimestamp indicating a particular point in time.

The present invention recognizes that, in some examples, a target nodemay only be capable of sending uplink messages at certain timeintervals, e.g. it may be restricted to sending uplink messagesperiodically in order to save power. Thus, by using timing informationof the first uplink message in order to calculate the timeout period,the timing capabilities of the target node can be taken into account.

A data size may, for example, indicate a size in bits or bytes of thefirst uplink message.

It is also recognized that a target node may be limited in the amount ofdata it is able to send over a period of time, e.g. in order to minimizepower. This may be taken into account by setting the minimum length ofthe timeout period based on the data size of a previous uplink message(to take account of a recovery period of the target node to be able tosend the uplink message).

Of course, particularly advantageous embodiment use both timinginformation and a data size of the first uplink message in order to setthe minimum timeout period. For example, a target node may be restrictedto sending a certain amount of data within a predetermined time period(e.g. limited duty cycle). Thus, a more accurate determination of whenthe target node is able to send a response uplink message (i.e. definingthe timeout period) may be determined by using both timing informationand a data size of the first uplink message.

The minimum timeout period may be calculated (further) using timinginformation of the downlink message.

Setting the minimum timeout period further based on timing informationof the downlink message enables a length of the timeout period that hasalready lapsed or how long the timeout period is expected to last fromthe time of sending the downlink message.

For example, it may be known that a target node is only able to sendmessages every minute (e.g. 12:01; then 12:02 etc.). By basing theminimum timeout period on the timing information of the downlinkmessage, it is possible to more accurately identify the predicted timeat which the target node is able to send the response uplink message,and therefore more accurately identify an appropriate length for thetimeout period.

Preferably, timing information of both the first uplink message and thedownlink message is used to determine the minimum timeout period. By wayof example, the length of the timeout period may be based on adifference between a time at which the first uplink message issent/received and a time at which the downlink message is sent. Thisenables an accurate determination of precisely when the target node isable to send the response uplink message (i.e. with respect to a time atwhich the downlink message was sent).

Timing information of the downlink message may include, for example, atime at which the downlink message is sent, a (predicted) time at whichthe downlink message is received by the target node, a length of timetaken to send downlink information and so on.

The minimum timeout period may be (further) based upon at least a datatransmission rate and/or a maximum allowable duty cycle of the wirelessnetwork.

In other words, characteristics of the wireless network may define thelength of the timeout period. In particular, the wireless network mayrestrict a communication capability of the target node, so that thetarget node is unable to send the response uplink message until acertain period of time after sending the first uplink message (the“recovery period”).

Thus, by basing the minimum timeout period on such characteristics ofthe wireless network, a time at which the target node is able to sendthe response uplink message (i.e. and thus the timeout period) can bemore accurately identified.

A data transmission rate and/or maximum allowable duty cycle areparticular examples of characteristics of the wireless network that mayrestrict a communicative capability of the target node, and thereforeprovide suitable measurements for establishing the timeout period.

The method may further comprise a step of calculating the minimumtimeout period based on at least one characteristic of the first uplinkmessage(s) sent by the target node. Thus, the minimum timeout period maybe actively calculated.

The step of calculating the minimum timeout period may comprise:determining a length of a recovery period, following the first uplinkmessage, during which the target node is not permitted to issue asubsequent uplink message in accordance with an operating practice;determining the minimum timeout period based on the length of therecovery period.

It is therefore proposed to determine a length of time (the “recoveryperiod”) taken by the target node to recover from the sending the firstuplink message before it is able to send a subsequent uplink message,e.g. the response uplink message. The recovery period thereforerepresents a period of time, since sending the first uplink message,that the target node is unable to send a further message. Thus, therecovery period may represent a length of time after the first uplinkmessage until the target is able to send the response uplink message.

The length of the recovery period may vary depending upon a number offactors, but is typically reliant on an operating practice of thewireless network and/or target node.

Optionally, the step of determining the minimum timeout periodcomprises: determining the length of an offset time period, being thelength of time between the sending of first uplink message and thesending of the downlink message; determining the minimum timeout periodbased on the offset time period and the recovery period.

This embodiment enables the minimum timeout period to be set furtherbased on a length of time between sending of the first uplink messageand the sending of the downlink message, i.e. the “offset time period”.

Thus, a period between the length of time between sending the firstuplink message and the sending of the downlink message may be taken intoaccount when calculating the minimum timeout period. In particular, anyof the recovery period that has already elapsed (“expired period”)before sending of the downlink message may be taken into account. Thus,embodiments may subtract the offset time period from the recoveryperiod, and determiner the minimum timeout period based the resultingvalue. This reduces the length of the minimum timeout period, therebyfurther improving a communicative speed of the wireless network.

In yet other examples, the minimum timeout period may be set to no lessthan the length of the recovery period. This may be performed for thesake of processing efficiency, and to increase a margin for the timeoutperiod (e.g. to minimize a risk of missing the uplink response message).

In some examples, the step of determining a length of a recovery periodcomprises: determining a data size of the first uplink message(s);determining a data transmission rate of the wireless network;determining a maximum allowable duty cycle of the wireless networkaccording to the operating practice; and determining the length of therecovery period based on the data size of the first uplink message, thedata transmission rate of the wireless network and the maximum allowableduty cycle of the wireless network.

Preferably, the step of determining the length of the recovery periodcomprises: determining the transmission time of the first uplinkmessage(s), being the length of time taken by the target node to sendthe first uplink message(s), based on the size of the first uplinkmessage(s) and the data transmission rate; and calculating the length ofthe recovery period based on the transmission time of the first uplinkmessage(s) and the maximum allowable duty cycle.

Thus, a method may comprise determining how long it takes (“transmissiontime”) for the first uplink message(s) to be communicated over thewireless network. The transmission time, together with the maximumallowable duty cycle, can indicate a length of a recovery period beforethe target node is able to communicate again.

This enables an accurate assessment of the length of the recovery period(which adheres to an operating practice), and thereby enables thetimeout period to be calculated based on the operating practice. A moreaccurate timeout period can therefore be obtained.

In some examples, the minimum timeout period is further based on aminimum round-trip time representing a minimum length of time taken,subsequent to the sending of a downlink message, to receive a responseuplink message.

By way of example, the minimum timeout period may be based on the normalor standard round-trip, representing a length of time taken for atypical downlink and response uplink cycle to occur. Thus, theround-trip time may represent a length of time taken (after sending ofthe downlink message) for the downlink message to pass to the targetnode through the wireless network, for the target node to process and(immediately) respond to the downlink message, and for the responseuplink message to return through the wireless network (i.e. a “normalround-trip time”). The round-trip time is independent of a length oftime for which the target node is unable to send communications (e.g.due to operating practices), i.e. independent of the recovery period.

In particular embodiments, an absolute minimum value for the length ofthe timeout period may be the round-trip time, so that the minimumtimeout period can be no less than the round-trip time. This ensuresthat the minimum timeout period takes into account communicative delay(e.g. wireless network delay), reducing the likelihood that a downlinkmessage will be unnecessarily resent.

In some embodiments, the minimum timeout period is set to be the greaterof the recovery period and the round-trip time previously described.

The method may further comprise, in response to receiving a seconduplink message, different to the response uplink message, from thetarget node after sending the downlink message and before receiving theresponse uplink message, recalculating the minimum timeout period usingat least one characteristic of the second uplink message.

Thus, the timeout period may be recalculated when a new uplink message(“second uplink message”) is received after sending of the downlinkmessage. Such an embodiment recognizes that a message flow may involvenumerous network elements (e.g. routers, gateways, message buffersetc.), which may mean that there is a delay after the target node sendsthe second uplink message. This delay could result in the downlinkmessage being sent after the target node has sent the second uplinkmessage, but before receiving the second uplink message.

The second uplink message may result in the target node being unable tocommunicate for an additional period of time (i.e. beyond the timeoutperiod calculated based on the first uplink message(s)). Thus,embodiments may comprise recalculating the timeout period based on oneor more characteristics of the second uplink message. Any describedmethod for calculating the timeout period based on one or morecharacteristics of the first uplink message(s) may be adapted forrecalculating the timeout period based on the second uplink message,mutatis mutandis.

The timeout period may be set to the determined minimum timeout period.In other examples, the timeout period may be set to the sum of adetermined minimum timeout period and an additional period (e.g.accounting for communicative delay through the wireless network).

There is also proposed a computer program comprising code means forimplementing any previously described claim when said program is run ona computer.

According to examples in accordance with an aspect of the invention,there is provided a communication unit for communicating with a targetnode of a wireless network. The communication unit comprises atransceiver adapted to send signals to and receive signals from thetarget node. The communication also comprises a processor adapted tocommunicate with the transceiver in order to: receive a first uplinkmessage(s) sent by the target node; subsequently send a downlink messageto the target node; determine whether the target node has responded tothe downlink message with a response uplink message within a timeoutperiod following the sending of the downlink message; and in response tothe target node failing to respond to the downlink message with aresponse uplink message within the timeout period, resend the downlinkmessage to the target node, wherein the timeout period is no less than aminimum timeout period calculated using at least one characteristic ofthe first uplink message(s) sent by the target node.

The minimum timeout period may be calculated using timing informationand/or a data size of the first uplink message.

There is also proposed a network system comprising: the communicationunit herein described; and at least one target node adapted to: send thefirst uplink message to the communication unit; receive the downlinkmessage from the communication unit; send a response uplink message tothe communication unit in response to the downlink message, wherein thetiming of sending the response uplink message to the communication unitis based on at least one characteristics of the first uplink message(s).

The network system preferably operates using an LPWAN technologystandard.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearlyhow it may be carried into effect, reference will now be made, by way ofexample only, to the accompanying drawings, in which:

FIG. 1 illustrates an example of a Low-Power Wide-Area Network;

FIGS. 2 to 5 provide timing diagrams indicating communications betweentwo nodes of a Low-Power Wide-Area Network;

FIG. 6 illustrates a method according to an embodiment; and

FIG. 7 illustrates a communication unit according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the Figures.

It should be understood that the detailed description and specificexamples, while indicating exemplary embodiments of the apparatus,systems and methods, are intended for purposes of illustration only andare not intended to limit the scope of the invention. These and otherfeatures, aspects, and advantages of the apparatus, systems and methodsof the present invention will become better understood from thefollowing description, appended claims, and accompanying drawings. Itshould be understood that the Figures are merely schematic and are notdrawn to scale. It should also be understood that the same referencenumerals are used throughout the Figures to indicate the same or similarparts.

According to a concept of the invention, there is proposed a method andcorresponding apparatus for communicating with a target node (e.g. aparticular device) of a wireless network. In particular, there is aconcept of more accurately identifying a timeout period during which thetarget node is expected to acknowledge a communication. The inventionrelies on a concept of providing a dynamic timeout period, the length ofwhich is based upon one or more characteristics of at least one mostrecent or previous communication from the target node.

Embodiments are at least partly based on the realization that theability of a target node to respond to an external communication may bereflected in characteristics of one or more previous communications sentby that target node. In particular, the length of a recovery period,being a period after sending a most recent communication during whichthe target node is unable to send further communications, can berepresented by characteristics of the communication or communicationsimmediately preceding the recovery period.

Illustrative embodiments may, for example, be employed in Low-PowerWide-Area Networks, and in particular to communicating with target nodesof Low-Power Wide-Area Networks that employ power saving practices oruse particular operating practices (such as limited duty cycles,periodic communications and so on). However, embodiments may beadvantageously used in any wireless network for which a target node hasa restricted communication capability (e.g. a low data transmission rateand/or restricted duty cycle).

The term “transmission time” (or “time-on-air”) refers to a length oftime that a communication takes to transmit over the wireless network toa destination. The transmission time can be calculated using a data sizeof the communication and a data transmission rate (i.e. bandwidth) ofthe network.

The term “duty cycle” refers to the proportion of time during which anode or device sends communications over the wireless network. Forexample, if within a 100 second period a device sends only a singlemessage taking 1s to transmit over the network, then the duty cycle ofthat device is 1%.

The term “restricted duty cycle” or “limited duty cycle” refers to themaximum allowable duty cycle for a given node or device. Suchrestrictions may be applied by operating practices, communicationstandards and so on. For example, if a target node has a restricted dutycycle of 1%, it is only able to send communications 1% of the time (e.g.for a total of 36 seconds in a 1 hour period).

If a node/device has a restricted duty cycle, this restriction may beapplied dynamically, over a moving window of time or within fixedperiodic intervals of time.

In a “dynamic restriction” mode, after sending a single communication, adevice may be unable to send a further communication until the dutycycle restriction/condition is met. For example, if a device following adynamic restriction mode takes 1 second to send a communication, and hasa restricted duty cycle of 1%, then it will be unable to send a furthercommunication for 99 seconds.

In a “moving window restriction” mode, the device may have a restrictedduty cycle within a moving window of a predetermined length. This wouldmean that there is a maximum combined transmission time for all messagessent by the device within any given window of the predetermined length(i.e. in a time period of the predetermined length beginning at anygiven point in time). For example, if a device (operating in a movingwindow restriction mode) has a restricted duty cycle of 1% with a timewindow of 1 hour, that device would be unable to send a desiredcommunication that would cause the device to send more than 36 secondsof communications within an immediately preceding 1 hour period—ratherthe device must wait until sending of the desired communication wouldnot cause the device to send more than 36 seconds of communication withan immediately preceding 1 hour period.

In a “periodic intervals restriction” mode, the device may have amaximum length of time (e.g. 36 seconds) for communicating within fixedperiodic intervals of a predetermined length (e.g. 1 hour). For example,the device (operating in the “periodic intervals restriction” mode) maycumulatively count a time spent sending communications, and preventfurther communications after a predetermined length of time (e.g. 36seconds) is spent sending communications. The cumulative count can thenbe reset at periodic intervals (e.g. every hour) to thereby enablecommunications to be sent again.

Precise restrictions on a duty cycle of a device, and how to implement arestricted duty cycle, may differ between in different implementations(e.g. different devices, different networks, different operatingpractices and/or different communication standards). Thus, there may bedifferent modes or method of restricting a duty cycle of a node ordevice.

FIG. 1 illustrates a Low-Power Wide-Area Network (LPWAN) 1, an exampleof a wireless network, and is illustrated to provide context forembodiments of the invention. Other wireless networks may also employthe concepts described in this description and be formed with a similararchitecture.

The illustrated LPWAN 1 comprises a network controller 2, and aplurality 3 of end nodes 4, 5, 6, 7. Each end node, including the firstend node, is managed by the network controller 2.

The network controller 2, alternatively named a server, communicateswith the end nodes 4, 5, 6, 7 over a wireless communication channelusing a LPWAN communication protocol. In some embodiments, the networkcontroller communicates with the end nodes via intermediary devices,such as a network server 8 and/or gateways 9. Such intermediary devicesmay, for example, be operated/owned by a different party to theowner/operator(s) of the network controller 2 and/or end nodes 4, 5, 6,7.

The network controller 2 may be capable of communicating with furtherdevices on other networks (not shown), e.g. through a router tocommunicate via the internet, Wi-Fi, Bluetooth® and so on.

The end nodes need not communicate with the network controller 2 viaonly a single gateway 9. Rather, messages from end nodes 4, 5, 6, 7 maybe sent via any one or more gateways 9 of the LPWAN 1 to the networkserver 8 and (thereafter to the) network controller 2. The networkserver 8 and/or the network controller 2 may be adapted to handle anyduplicated messages received from a plurality of gateways. In otherembodiments, the network controller 2 communicates directly with the endnodes 4, 5, 6, 7, i.e. there are no intermediary devices.

In this way, the network controller 2 can communicate with the endnodes, and is able to manage the end nodes. Preferably, each end node 4,5, 6, 7 in at least the group 3 of end nodes is managed in a same orsimilar manner as other end nodes in the group of end nodes.

Purely by way of example, each end node 4, 5, 6, 7 may be a controllableluminaire, and the network controller 2 may be a user-controllable hubfor controlling output characteristics of the luminaires. Messages fromthe end node to the network controller may include, for example, regularstatus updates (e.g. detailing current output characteristics, such as acurrent intensity/color/temperature of light), responses to enquiries oracknowledgment of commands. Messages from the network controller to theend nodes may include commands for controlling output characteristics orrequesting certain information.

Communications within the LPWAN are conducted using a known LPWANwireless communication standard or LPWAN communication protocol, such asLoRaWAN or ETSI's Low Throughput Networks (LTN).

Proposed methods relate to a concept of communicating with a target nodeof the LPWAN 1, such as one of the end nodes 4, 5, 6 7. Such a conceptmay be employed, for example, by the network controller 2 to control itscommunications with any of the end nodes 4, 5, 6, 7. Of course, othernodes of the LPWAN may use the proposed concept to advantage, e.g. tocontrol communications between different end nodes, network servers 8,gateways 9 and/or network controllers 2. Thus, any element of the LPWANcan act as the target node, and any element able to communicate with anelement of the LPWAN (including devices external to the LPWAN) can actas a communication unit (being the unit/module/device that performs theherein described method of communicating with the target node).

In particular, proposed methods may be performed by devices external tothe LPWAN (e.g. communicating via the network controller) forcommunicating with a node of the LPWAN. Such embodiments may extend toother wireless networks than a LPWAN.

However, for the sake of clarity, hereafter described examples willrelate to methods for controlling a communication between the networkcontroller 2 (an example of a “communication unit”) and an end node 4(an example of a “target node”) of the LPWAN 1.

An “uplink message” is a message that is sent from the target node (e.g.where the target node is an end node of a LPWAN: a communication fromthe end node to the network controller). A “downlink message” is amessage that is sent to the target node (e.g. where the target node isan end node of a LPWAN: a communication from the network controller tothe end node). The term “message” is used to refer to any instance ofcommunication between nodes of a wireless network, and may be formed ofa single packet.

As previously discussed, there is a desire to reduce a power consumptionin wireless networks (and especially LPWANs). One way of achieving thisis to limit a rate of communications between nodes of the wirelessnetwork, and in particular to communications from end nodes.

This can be achieved, for example, by limiting some nodes to only beingcapable of sending communications at periodic intervals or limiting aduty cycle of communications sent by said nodes. There are other reasonsfor limiting a duty cycle of communications, for example, to give othernodes and systems a chance to use a same channel or spectrum forcommunications. This is especially important in the unlicensedcommunications spectrum, and such duty cycle restrictions are commonlyset in regulations or communication protocols/standards.

Such methods can effectively introduce a “recovery period” t_(r) intothe said node, being a period following sending of a communication orcumulative communications that the node is unable to send furthercommunications. Thus, a recovery period indicates a length of timefollowing sending of a message that a node during which the same node isunable to send a further message (in order to adhere to a particularcommunication protocol/standard or operating practice).

By way of example only, the LoRaWAN communication protocol limits theduty cycle of communications sent by a node of the LPWAN to 1% in theEU868 band. As, the data transmission rate of a LPWAN protocol isusually low, e.g. a typical data transmission rate of LoRaWAN is from250 bps to 5470 bps in the EU868 band, this can result in thetransmission time of a communication from a node taking between hundredsof milliseconds to more than one second. This would mean, in an examplewhere the transmission time is 1 second, that the duty cycle restrictionprevents a LoRaWAN node may not send two packets in 100 seconds. In somecases, such a restriction prevents a node from communicating for morethan 36 seconds in one hour.

Thus, in an example where a “dynamic restriction mode” (previouslydescribed) is used, there is a recovery period of 99 seconds followingthe sending of a first communication by the node before a secondcommunication can be sent.

In an example where a “moving window restriction mode” (previouslydescribed) is used, having a moving window 1 hour in length, there is arecovery period introduced after the sending of a message that causesmore than 36 seconds of cumulative transmission time by that node withina preceding 1 hour period. The recovery time represents the length oftime until a time point at which, for the hour preceding that timepoint, there is less than 36 seconds of cumulative transmission time.

By way of another example, not involving duty cycle restrictions, acommunication protocol may restrict certain nodes (e.g. end nodes) toonly being able to communicate at periodic intervals (e.g. every hour,every minute and so on). Thus, there may be a recovery period aftersending a first communication before a second communication can be sentby that same node.

By way of yet another example, a communication protocol may restrict adata usage of certain/target nodes, preventing them from sending morethan a certain amount of data within a predetermined time period, i.e.defines a data usage limit. Thus, after sending a large message orpacket (or series of packages cumulatively exceeding the data usagelimit), a target node may be unable to send communications until arecovery period has elapsed.

The recovery period of a node introduces difficulties if a downlinkmessage, such as a downlink command, to that node requires anacknowledgement or response. This is because senders of such downlinkmessages typically set a timeout period t_(to) for the response, afterwhich the downlink message will be resent. The purpose of such a timeoutperiod is to ensure that a target node receives a downlink message, e.g.as is common in handshake protocols. It is herein recognized that if thetimeout period expires before the end of the recovery period, this couldresult in an unnecessary additional message(s) being sent to the node(having the recovery period) even though the earlier downlink messagehas been successfully received. This would disadvantageously increasetraffic on the network.

An example of this issue can be understood with reference to FIG. 2.FIG. 2 provides a diagram illustrating communications between a networkcontroller 21 and an end node 22 over a period of time t. In particular,FIG. 2 illustrates times at which example communications are sent by anetwork controller 21 (i.e. a downlink message) and an end node 22 (i.e.an uplink message).

The end node 22 is subject to communication restrictions, thereby havinga recovery period t_(r) after sending a message. The network controller21 is adapted to resend a message, such as a command or instruction, tothe end node 22 after a timeout period t_(to) has elapsed in order tofollow a handshake protocol.

The scenario illustrated in FIG. 2 is that the end node 22 has sent afirst uplink message u₂₁ shortly before receiving a first downlinkmessage d₂₁. As a result of the recovery period t_(r) (earlierdiscussed), the end node 22 is unable to respond, i.e. with a responseuplink message u₂₂, until the recovery period t_(r) has elapsed.

It will be clear that in the event that the timeout period t_(to)associated with the first downlink message d₂₁ expires before the timeat which the recovery period t_(r) has elapsed and a response uplinkmessage u₂₁ is sent, as illustrated, this would result in a seconddownlink message d₂₂ (e.g. replicating the information of the firstdownlink message) being sent to the end node. Thus, unnecessary traffichas been added to the LPWAN (as the information will be unnecessarilyresent to the end node).

The inventors have appreciated the need to appropriately set a timeoutperiod to avoid unnecessary resending of a downlink message to a targetnode, whilst also avoiding excessively long timeout periods which woulddisrupt/delay communications. Without employing the method disclosed inthis application, the timeout period would need to be set to anextremely long period of time (e.g. 150 seconds or the maximum possiblelength of the response period) to ensure that a target node is able tosend a response to a downlink message before the timeout period elapses.This would result in significant communication delays and reducedcommunication certainty, and is not considered to be user friendly.

Of course, the skilled person would also appreciate the benefit ofdetermining the timeout period without necessitating the resending of adownlink message. This could be done, for example, to monitor traffic onthe network or to control sending of additional downlink messages to atarget node (e.g. if a series of downlink messages is to be sent).

FIG. 3 illustrates a timing diagram illustrating communications betweena network controller 31 and a target node 32 over a period of time taccording to an embodiment of the invention.

The length of the timeout period t_(to), associated with a downlinkmessage d₃₁ sent to the target node 32, is determined based oncharacteristics of only a most recent (to the downlink message d₃₁)uplink message u₃₁ sent by the target node 32. In particular, a minimumlength of the timeout period t_(to) is based on or determined usingcharacteristics of the uplink message u₃₁, which minimum length may thenbe used to set or determine the length of the timeout period t_(to). Ithas been herein recognized that characteristics of the most recentuplink message u₃₁ can (depending upon the operating practice orcommunication protocol) define a length of the overall recovery periodt_(r).

The timeout period t_(to) may be determined by calculating the recoveryperiod t_(r), determining how much of the recovery period t_(r) haselapsed at the time of sending the downlink message d₃₁ (i.e.determining a length of an expired period t₁), and determining a minimumlength of the timeout period t_(to) based on (e.g. equal to) theremaining time of the recovery period (i.e. determining a length of anunexpired period t₂).

The expired period t₁ can also be called the offset time period, beingthe length of time between the sending of the uplink message and thesending of the downlink message.

In preferable embodiments, an additional length of time t_(a), e.g.representing a delay for preparing and/or sending a communication fromthe target node 32 to the network controller 31, may be added to thelength of the unexpired interval t₂ in order to calculate the minimumlength of the timeout period. Delays may be caused, for example, by therouting of the response uplink message sent by the target node or bybuffers in the LPWAN. Thus, there may be a delay between sending of theresponse uplink message u₃₂ and it being received by the networkcontroller 31.

Adding the additional length of time t_(a) onto the length of theunexpired period t₂ more accurately determines a length of time takenfor a response uplink signal u₃₂ to be generated and sent by the targetnode (taking into account communicative restrictions) and to propagatethrough the network. This further avoids a likely that the downlinkmessage will be resent unnecessarily.

The length of the additional length of time may be set, for example, tothe length of a minimum round-trip time, later described. In otherexamples, the length of the additional length of time may be based on adifference between a time at which the first uplink message u₃₁ was sent(e.g. as contained in a timestamp accompanying the first uplink message)and a time at which the first uplink message was actually received.Other suitable methods of establishing a suitable additional length oftime will be apparent to the skilled person (e.g. by consultingliterature for the network or from known operating practices).

Thus, timing information of both the uplink message u₃₁ and the downlinkmessage d₃₁ may be used to calculate how much t₁ of the recovery periodt₂ has elapsed at the time of sending the downlink message d₃₁, therebycalculating an expired period t₁ and an unexpired period t₂ of therecovery period t_(r). The minimum length of the timeout period t_(to)is set to be no less than the unexpired period of the recovery periodt_(r).

In particular examples, the minimum length of the timeout period t_(to)is set to be equal to the length of the unexpired period of the recoveryperiod t_(r) plus an additional length of time t_(a) representing atleast a length of a delay for the response uplink message u₃₂ topropagate through the network (i.e. representing latency).

A first method of determining the length of the recovery period t_(r)could be to use information on the data size of the uplink message u₃₁,a known data transmission rate or bandwidth (e.g. in bits per second) ofthe LPWAN and a duty cycle restriction of the LPWAN (e.g. according toan operating practice or LPWAN communication protocol). In particular, atransmission time of the uplink message and a duty cycle restriction canbe used to calculate the recovery period.

A transmission time of the uplink message u₃₁ can be readily calculatedusing the data transmission rate and the data size of the uplink messageu₃₁. For example, if the data size of the uplink message u₃₁ is 40bytes, and the data transmission rate is 250 bps (250 bits per second),the transmission time of the uplink message u₃₁ is 1.28 seconds(40*8/250). Here, the value 8 represents a conversion from bytes tobits.

The calculated transmission time and the duty cycle restriction can thenbe processed to determine the length of the recovery period t_(r). Forexample, assuming a “dynamic restriction” approach is taken forrestricting a duty cycle of the target node 32, if the transmission timeis 1.28 seconds, and the duty cycle restriction is 1% (i.e. signals fromthe node can only be on the air, on average, 1% of the time), the lengthof the recovery period t_(r) is approximately 128 seconds.

A second method of determining the length of the recovery period t_(r)could be to determine a length of time between allowable periodiccommunications of the target node. For example, some communicationprotocols may restrict communications from certain nodes (such as endnodes) to only being periodic or at regular intervals. The length of therecovery period t_(r) may be set to the length of the periodic interval.

A third method of determining the length of a recovery period t_(r)could be to determine a length of the recovery period based only on adata size of the first uplink message. For example, there may be a knownrelationship between data size and length of a recovery period, whichrelationship may depend upon the communication protocol of the LPWAN(e.g. setting data limits).

It will be appreciated that the method used to calculate the recoveryperiod may depend upon the operating practice or communication protocolof the LPWAN, and may therefore differ in different implementations ofthe concept.

However, it is particularly advantageous to use embodiments in which atleast a duty cycle restriction of the LPWAN is taken into account. Suchembodiments are advantageous as the duty cycle restriction tends to varybetween different locations (e.g. the EU may have a different duty cyclerestriction to the US) and between different frequency bands (e.g. 10%in a 869.4-869.65 MHz frequency band and 1% in a 868.0-868.6 MHzfrequency band according to the regulation of ETSI), and it would beadvantageous to use an adaptable method for different scenarios. It isconsidered that one particularly innovative aspect of this invention isthe use of a duty cycle restriction to calculate a recovery period.

Preferably, the minimum length of the timeout period is further based ordetermined using a minimum round-trip time. The minimum round-trip timerepresents a minimum length of time for the downlink message to be sentto the target node, for the target node to process the downlink messageand for the response uplink message to be returned to the sender of thedownlink message. Thus, the minimum round-trip time represents a‘normal’ length of a message and response cycle (assuming that thetarget node has no restrictions on its communications).

The minimum round-trip time may be calculated, for example, bydetermining a difference between a timestamp of sending a downlinkmessage to a target node to a timestamp of receiving a response uplinkmessage (to the downlink message) from the target node, when it is knownthat the target node is able to communicate freely (i.e. it is not in arecovery period). Such a state of the target node could be achieved byfirst instructing the target node to not send any communications for apredetermined period of time, such as a maximum possible recoveryperiod.

In particular examples, if the recovery period has expired (or the timeleft to the end of the recovery period is less than the minimumround-trip time), the minimum length of the timeout period is set to noless than the minimum round-trip time. The minimum round-trip time maytherefore represent an absolute minimum value of the timeout period.

In other words, the minimum length of the timeout period may be set tothe greater of the minimum round-trip time and the unexpired period t₂of the recovery period t_(r).

A length of the timeout period is set to be no less than the determinedminimum length of the timeout period. For example, the length of thetimeout period may be set to be equal to the determined minimum lengthof the timeout period.

In other examples, e.g. to introduce a margin for error or unexpectedcommunicative delay, a length of the timeout period may be calculatedusing the determined minimum length. In one example, a predeterminedperiod of time (e.g. 500 ms, 1 second or 5 seconds or the minimum roundtrip time) may be added onto the determined minimum length to calculatethe length of the timeout period. In another example, the determinedminimum length is multiplied by a predetermined value (e.g. any valuebetween 1 and 2, such as 1.1 or 1.5) to calculate the length of thetimeout period.

Other methods of calculating an appropriate length of the timeoutperiod, based on the determined minimum length of the timeout period,will be readily apparent to the skilled person. Thus, the length of thetimeout period is based on the minimum length of the timeout period.

In some simpler embodiments, calculation of the expired and/or unexpiredperiod of the recovery period is omitted, and the minimum value for thetimeout period can be set based solely on the length of the recoveryperiod. For example, the timeout period may be set to be equal to thelength of the calculated recovery period or the recovery period plus anadditional length of time t_(a) representing at least a length of adelay for the response uplink message to propagate through the network(i.e. representing latency), which may be approximated using the minimumround trip time.

Thus, in some embodiments, calculation of the recovery period forms thedetermination of the minimum length of the timeout period. Suchembodiments may minimize a processing power required to calculate thetimeout period, at the expense of having a potentially longer timeoutperiod (i.e. and increasing communication delay and communicationcertainty).

In some embodiments, a method may be adapted to recalculate the timeoutperiod based on one or more characteristics of a second uplink message,if that second uplink response is received during the timeout periodt_(to) and does not correspond to the response uplink message. Thus, thetimeout period may be effectively reset if a second uplink message isreceived after sending of a downlink message (assuming the second uplinkmessage is not a response to the downlink message).

One such embodiment is illustrated in FIG. 4, which is a diagram againillustrating communications between a network controller 41 and a targetnode 42 over a period of time t according to an embodiment of theinvention.

In particular, FIG. 4 illustrates times at which the target node 42sends uplink messages to the network controller 41 and times at whichthe network controller sends downlink messages to the target node. Forthe sake of improved clarity, FIG. 4 also illustrates time at whichuplink messages are received by the network controller (having referencenumerals with the prefix r-u).

In the illustrated scenario, the target node sends a first uplinkmessage u₄₁ and a second uplink message u₄₂ successively. The networkcontroller 42 sends a downlink message d₄₁ after the first uplinkmessage u₄₁ is received (at a first time r-u₄₁), but before the seconduplink message u₄₂ is received (at a second time r-u₄₂).

Initially, the timeout period t_(to −1), based on one or morecharacteristics of the first uplink message u₄₁, using a methodpreviously described (e.g. when the target node 42 is operating in the“dynamic restriction” mode). This is because the network controller isunaware of the second uplink message u₄₂, as it has not yet beenreceived.

Subsequently during the timeout period t_(to −1), the second uplinkmessage u₄₂ is received. In accordance with the embodiment, the timeoutperiod is then recalculated, to form new timeout period t_(to −2), basedon one or more characteristics of the second uplink message u₄₂.Previously described methods of calculating a timeout period may beused. Without the step of re-calculating the timeout period t_(to −2), aresponse uplink message u₄₃ would be received after the initial timeoutperiod t_(t0-1) (calculated based on the first uplink message u₄₁) hasexpired, because there would be a recovery period t_(r) following thesending of the second uplink message u₄₂. This could disadvantageouslylead to the downlink message d₄₁ being resent unnecessarily, as thedownlink message d₄₁ may have been successfully received by the targetnode 42.

Thus, by recalculating or resetting the timeout period based on one ormore characteristics of a second uplink message u₄₂ (received during theinitial timeout period t_(to −1)) avoidance of unnecessary resending ofthe downlink message can be achieved.

It should be clear that the second uplink message u₄₂ must bedistinguished from a response uplink message u₄₃ in that the seconduplink message u₄₂ is not sent in response to the downlink message d₄₁.Typically, this would mean that the second uplink message u₄₂ was sentby the target node before the downlink message d₄₁ was sent by thenetwork controller and/or received by the target node.

FIG. 5 illustrates a timing diagram illustrating communications betweena network controller 51 and a target node 52 over a period of time taccording to another embodiment of the invention.

In this embodiment, the target node 52 has a restricted duty cycle thatoperates in a “moving window restriction” mode, as compared to the“dynamic restriction” mode used in FIGS. 3 and 4.

Thus, the target node 52 is unable to send communications that wouldlead to a combined transmission time (within an immediately precedingpredetermined period at any time point) being greater than a maximumcombined transmission time. For example, where the restricted duty cycleis 1% and the predetermined period is 1 hour, the maximum combinedtransmission time is 36 seconds.

The minimum timeout period can be calculated using the following method.

The total (i.e. cumulative or combined) transmission time of all uplinkmessages u₅₁, u₅₂, u₅₃ sent by the target node 22 in a predeterminedperiod t_(res) (e.g. 1 hour) before the sending of the downlink messaged₂₁ is calculated. The transmission time of each uplink message may becalculated using any previously described method (e.g. using the datasize of each uplink message and the data transmission rate of thenetwork).

If the total transmission time is less than the maximum combinedtransmission time, then the minimum timeout period can be set to beequal to zero or a minimum round-trip time (previously described). Thisis because the target node can immediately send a communication withoutcontravening the duty cycle restriction.

If the total transmission time is greater than or equal to the maximumcombined transmission time, then the minimum timeout period is set sothat, at the expiry of the minimum timeout period from a current pointin time, the combined transmission time in a predetermined periodimmediately preceding the expiry of the timeout period is less than themaximum combined timeout period. This may be performed, for example, bysetting the minimum timeout period to being no less than a differencet_(d) between a start time t_(st) of the predetermined period t_(res)(relative to the downlink message) and the time at which the earliestfirst uplink message u₅₁ (within the predetermined period t_(res)) wassent. Thus, the difference t_(d) can be considered to represent anunexpired length of a recovery period.

The timeout period may be determined from the minimum timeout periodusing any previously described method (e.g. adding an additional lengthof time).

The embodiment described with reference to FIG. 5 demonstrates how thecharacteristics (e.g. time of sending and data size) of more than onefirst uplink message sent previous to the downlink message can be takeninto account when determining the length of the recovery period t_(r)and/or the timeout period t_(to).

The skilled person will appreciate that the embodiment described withreference to FIG. 5 can be easily adapted to recalculate a new timeoutperiod based on one or more characteristics of second uplink messagereceived after sending of the downlink message. For example, a totaltransmission time may be calculated further using characteristics of thesecond uplink message.

As previously discussed, embodiments have been described in the contextof a network controller sending a downlink message to an end node(acting as the target node). However embodiments may be adapted toreplace the network controller with any other component of the wirelessnetwork (or other connected network) capable of sending a downlinkmessage to a component of the wireless network, and to replace the endnode with any other component of the wireless network capable of sendingan uplink message to another component of the wireless network or otherconnected network.

Embodiments of described methods have been described with reference totiming diagrams. Nonetheless, for the sake of clarity, a full flow chartillustrating a method according an embodiment is shown in FIG. 6.

FIG. 6 thus illustrates a method 60 of communicating with a target nodeof a wireless network, such as a Low-Power Wide-Area Network, LPWAN.

The method comprises a step 61 of receiving at least one first uplinkmessage sent by the target node. The method also comprise a step 62 ofsubsequently sending a downlink message to the target node, so that thedownlink message is sent after the at least one first uplink message isreceived (but not necessarily in response thereto).

It should be made clear that the first uplink message includes at leastthe most immediately preceding uplink message (in time) that wasreceived before the downlink message was sent. Thus, the first uplinkmessage includes at least the temporally closest uplink message that wasreceived before the downlink message was sent.

The method also comprises a step 63 of calculating a minimum timeoutperiod using at least one characteristic of the at least one firstuplink message, the minimum timeout period representing a minimum lengthof time following the sending of the downlink message during which thetarget node is expected to respond with a response uplink message. Thereis also a step 64 of determining a timeout period based on the minimumtimeout period.

The method also comprises a step 65 of determining whether the targetnode has responded to the downlink message with a response uplinkmessage within the timeout period following the sending of the downlinkmessage.

In some examples, in response to the target node failing to respond tothe downlink message with a response uplink message within the timeoutperiod, the method comprises a step 66 of resending the downlink messageto the target node. The method can then ends in a step END. Inembodiments, in response to the target node responding with a responseuplink message within the timeout period, the method could also then endin step END. However, step 66 is optional, and may be omitted, as theremay be other purposes for determining the timeout period.

The timeout period is no less than a minimum timeout period calculatedusing at least one characteristic of at least one first uplink messagesent by the target node.

In at least one example, the length of the timeout period is displayedor otherwise provided to a user. In particular examples, the remainingand/or elapsed time of the timeout period is displayed otherwiseprovided to a user. This may be performed using any audio, visual orhaptic/sensory feedback system, such as a screen/display, speaker orvibration system.

The skilled person would be readily capable of developing acommunication unit for carrying out a described method. Thus, each stepof the flow chart may represent a different action performed by acommunication unit, and may be performed by different modules of thecommunication unit.

FIG. 7 illustrates a network system 70 according to an embodiment of theinvention. The network system 70 comprises a communication unit 71according to an embodiment. The communication unit is adapted forcommunicating with a target node 72 of a wireless network, such as aLow-Power Wide-Area Network, LPWAN.

In particular, the communication unit comprises a transceiver 73 adaptedto send signals to and receive signals from the target node 72. This maybe performed, for example, using a wireless network such as thatdescribed in FIG. 1. Thus, the communication unit may, for example, actas a network controller.

The communication unit 71 also comprises a processor 74 adapted tocommunicate with the transceiver 73 in order to receive a first uplinkmessage sent by the target node 72; subsequently send a downlink messageto the target node; calculate a minimum timeout period using at leastone characteristic of the at least one first uplink message, the minimumtimeout period representing a minimum length of time following thesending of the downlink message during which the target node is expectedto respond with a response uplink message; determine a timeout periodbased on the minimum timeout period; and determine whether the targetnode has responded to the downlink message with a response uplinkmessage within the timeout period following the sending of the downlinkmessage.

Preferably, the minimum timeout period is calculated using timinginformation and/or a data size of at least one the first uplink message.Preferably, the minimum timeout period is calculated further using aduty cycle restriction of the wireless network or target node.

The communication unit 71 may further comprise a display (not shown)adapted to provide a user with an indication of the timeout periodand/or a remaining/elapsed time of the timeout period. This improves auser's understanding of the timeout period.

The target node 72 is adapted to send the first uplink message to thecommunication unit 71; receive the downlink message from thecommunication unit; and send a response uplink message to thecommunication unit in response to the downlink message, wherein thetiming of sending the response uplink message to the communication unitis based on at least one characteristics of the first uplink message.

Although only one target node is illustrated and described, embodimentsmay comprise more than one target node.

In preferable embodiments, a target node is a luminaire or light sourceadapted to be controllable by downlink messages, which preferably formsan end node. In particular, downlink messages may define outputcharacteristics of the luminaire or light source, such as a light outputintensity, color, temperature, angle, spread, direction or duration.

Preferably, the target node is a battery powered devices,resource-restricted unit, or power-harvesting device, such as asolar-powered devices. Such devices benefit from power saving practices,such as having restricted communications (e.g. limited duty cycletransmissions).

Preferably, a communication unit may be installed in a networkcontroller or other device adapted to control an operation of at leastone target node in a wireless network. Examples of suitable networkcontrollers or other devices include a wall switch; a touch panel; aremote control; and an occupancy sensor. Such embodiments areparticularly advantageous when the target or end nodes compriseluminaires or light sources.

In embodiments, a target node may be an input/output unit, which ispreferably an end node. Generally, the term “input/output unit”indicates that the unit is adapted to output sensory or controlinformation externally to the target node (e.g. output light, sound,touch etc. or control a pacemaker, medicinal drip etc.) and/or determineinformation about the node or its immediate environment (e.g.temperature, ambient light, power usage, presence of certain gases,water flow/usage, electricity flow/usage, pulse rate of a user and soon). Thus, the input/output unit may, for example, comprise awater/electricity meter, a temperature sensor, a moisture sensor, a gassensor, a pulse rate monitor and so on.

As discussed above, embodiments make use of a processor. The processorbe implemented in numerous ways, with software and/or hardware, toperform the various functions required. A processor is one such examplewhich employs one or more microprocessors that may be programmed usingsoftware (e.g., microcode) to perform the required functions. Aprocessor may however be implemented with or without employing aprocessor, and also may be implemented as a combination of dedicatedhardware to perform some functions and a processor (e.g., one or moreprogrammed microprocessors and associated circuitry) to perform otherfunctions.

Examples of processor components that may be employed in variousembodiments of the present disclosure include, but are not limited to,conventional microprocessors, application specific integrated circuits(ASICs), and field-programmable gate arrays (FPGAs).

In various implementations, a processor may be associated with one ormore storage media such as volatile and non-volatile computer memorysuch as RAM, PROM, EPROM, and EEPROM. The storage media may be encodedwith one or more programs that, when executed on a computer, one or moreprocessors and/or a processing arrangement, perform the requiredfunctions. Various storage media may be fixed within a processor or maybe transportable, such that the one or more programs stored thereon canbe loaded into a processor.

It will be understood that disclosed methods are preferablycomputer-implemented methods. As such, there is also proposed theconcept of computer program comprising code means for implementing anydescribed when said program is run on a computer. Thus, differentportions, lines or blocks of code according to an embodiment may beexecuted by a processor/computer to perform a herein described methods.

Variations to the disclosed embodiments can be understood and effectedby those skilled in the art in practicing the claimed invention, from astudy of the drawings, the disclosure and the appended claims. In theclaims, the word “comprising” does not exclude other elements or steps,and the indefinite article “a” or “an” does not exclude a plurality. Theterm “at least one of the following” means any combination of featuresfollowing this term, e.g. “at least one of the following: A, B and C”would mean “A and/or B and/or C”. A single processor or other unit mayfulfill the functions of several items recited in the claims. The merefact that certain measures are recited in mutually different dependentclaims does not indicate that a combination of these measures cannot beused to advantage. A computer program may be stored/distributed on asuitable medium, such as an optical storage medium or a solid-statemedium supplied together with or as part of other hardware, but may alsobe distributed in other forms, such as via the Internet or other wiredor wireless telecommunication systems. Any reference signs in the claimsshould not be construed as limiting the scope.

The invention claimed is:
 1. A method of communicating with a target node of a wireless network, the method comprising: receiving at least one first uplink message sent by the target node; subsequently sending a downlink message to the target node; calculating a minimum timeout period using at least one characteristic of the at least one first uplink message, the minimum timeout period representing a minimum length of time following the sending of the downlink message during which the target node is expected to respond with a response uplink message; determining a timeout period based on the minimum timeout period; and determining whether the target node has responded to the downlink message with a response uplink message within the timeout period following the sending of the downlink message.
 2. The method of claim 1, wherein each at least one characteristic comprises timing information, a data size and/or a transmission time of a first uplink message.
 3. The method of claim 1, wherein the minimum timeout period is calculated further using timing information of the downlink message.
 4. The method 1, wherein the minimum timeout period is calculated further using a duty cycle restriction of the wireless network or target node.
 5. The method of claim 4, wherein the at least one characteristic comprises timing information and a transmission time of each at least one first uplink message, and the step of calculating the minimum timeout period comprises: calculating, based on the duty cycle restriction and the at least one characteristic of the at least one first uplink message, a length of time before the target node is able to send an uplink message; and determining the minimum timeout period based on the calculated length of time before the target node is able to send a communication.
 6. The method of claim 1, wherein the step of calculating the minimum timeout period comprises: determining a length of a recovery period, following a most recent first uplink message, during which the target node is not permitted to issue a subsequent uplink message in accordance with an operating practice; and determining the minimum timeout period based on the length of the recovery period.
 7. The method of claim 6, wherein the step of calculating the minimum timeout period comprises: determining the length of an offset time period, being the length of time between the sending of the most recent uplink and the sending of the downlink message; calculating the minimum timeout period based on the offset time period and the recovery period.
 8. The method of claim 6, wherein the step of determining a length of a recovery period comprises: determining a data size of the most recent uplink message; determining a data transmission rate of the wireless network; determining a maximum allowable duty cycle of the wireless network or target device according to the operating practice; and determining the length of the recovery period based on the data size of the most recent first uplink message, the data transmission rate of the wireless network and the maximum allowable duty cycle of the wireless network.
 9. The method of claim 8, wherein the step of determining the length of the recovery period comprises: determining the transmission time of the most recent first uplink message, being the length of time taken by the target node to send the most recent first uplink message, based on the size of the most recent first uplink message and the data transmission rate; and calculating the length of the recovery period based on the transmission time and the maximum allowable duty cycle.
 10. The method of claim 1, wherein the minimum timeout period is further based on a minimum round-trip time representing a minimum length of time taken, subsequent to the sending of a downlink message, to receive a response uplink message.
 11. The method of claim 1, further comprising, in response to receiving a second uplink message, different to the response uplink message, from the target node after sending the downlink message and before receiving the response uplink message, recalculating the minimum timeout period using at least one characteristic of the second uplink message.
 12. The method of claim 1, further comprising, in response to the target node failing to respond to the downlink message with a response uplink message within the timeout period, resending the downlink message to the target node.
 13. A non-transitory computer readable medium comprising code means for implementing the method of claim 1 when the code is executed by a computer.
 14. A wireless network comprising: the communication unit of claim 13; and at least one target node adapted to: send the first uplink message to the communication unit; receive the downlink message from the communication unit; send a response uplink message to the communication unit in response to the downlink message, wherein the timing of sending the response uplink message to the communication unit is based on at least one characteristic of the first uplink message.
 15. A communication unit for communicating with a target node of a wireless network, the communication unit comprising: a transceiver adapted to send signals to and receive signals from the target node; a processor adapted to communicate with the transceiver in order to: receive at least one first uplink message sent by the target node; subsequently send a downlink message to the target node; calculate a minimum timeout period using at least one characteristic of the at least one first uplink message, the minimum timeout period representing a minimum length of time following the sending of the downlink message during which the target node is expected to respond with a response uplink message; determine a timeout period based on the minimum timeout period; and determine whether the target node has responded to the downlink message with a response uplink message within the timeout period following the sending of the downlink message. 